This invention relates to a method for producing aqueous emulsions and latices of sulfonated low unsaturation elastomers. More particularly, the invention relates to an improvement in carrying out the passivation or quenching of the elastomer cement sulfonation reaction in order to produce a more readily emulsifiable product and provide a more efficient overall latex process.
Sulfonated ionomers of butyl rubber and ethylenepropylene-diene terpolymers are known and are described, for example, in U.S. Pat. No. 3,642,728, issued Feb. 15, 1972 to Canter.
Latices prepared from sulfonated butyl rubber are disclosed in U.S. Pat. No. 3,770,682 issued Nov. 6, 1973 to Hubbard et al wherein the acid form of the sulfonated butyl rubber is emulsified using a nonionic surfactant. O'Farrell, U.S. application Ser. No. 487,907, filed July 12, 1974, now U.S. Pat. No. 3,912,683 issued Oct. 14, 1975, also relates to sulfonated butyl rubber latices and deals with the emulsification of neutralized sulfonated butyl rubber with an anionic surfactant. O'Farrell et al., in U.S. Pat. No. 3,836,511 issued Sept. 17, 1974 and in U.S. application Ser. No. 510,392, deal with the acyl sulfate sulfonation of these elastomers.
In the aforesaid techniques for preparing sulfonated elastomeric latices, substantial quantities of alcohol, such as n-propanol, have been required to quench or passivate the sulfonation reaction. This passivation step is essential in order to provide an emulsifiable product which can be further processed to give an acceptable latex. The amount of such alcohols used has been on the order of 20-40% by weight based on the weight of the sulfonated elastomer cement. After removing solvent, alcohol and excess water from the initial latex to form the final latex, the presence of these quantities of alcohol requires extensive distillation and purification procedures in order to separate the solvent, alcohol and water. When alchols, such a 1-octanol, having boiling points sufficiently high, such that they are not removed during solvent stripping and concentration of the latex, have been used, these alcohols remain as components of the finished latex and cause excessive coagulation and other instability problems in the finished product.
Another disadvantage with respect to the use of an alcohol quenching agent has been the requirement that fairly substantial amounts of emulsifier, such as 10 to 15 parts per hundred (phr), be used per hundred parts of sulfonated elastomer present in the cement. It is known that alcohols can have an adverse effect on the surfactant properties of anionic emulsifiers.